Radioactive alloy



Aug. 26, 1941.

J. H. DILLON RADIOACTIVE ALLOY Filed July 30, 1940 2 Sheets-Sheet 1 INVENTOR JbH/V H. 0/44 ON ATTORNEYS Aug. 26, 1941.

SEPARATING RADIUM D AND J. H. DILLON RADIOACTIVE ALLOY Filed July 30, 1940 TREATING RADIUM D- LEADRESIDUE TO PRODUCE RADIUM D AND LEAD CHLORIDES AGING RADIUM D AND LEAD CHLORIDES 2 Sheets-Sheet 2 LEAD CHLORIDES TITRATI NG- MOTHER LIQUOR TO 0.05 NORMAL HYDROCHLORIC ACID TO DEVELOP POLONIUM ADDING AGED RADIUMD POLONIUM AND LEAD CHLORIDES TO TITRATED LIQUOR PREPARING LIQUOR OFAGED RADIUM D POLONIUM ANDLEAD CHLORIDES COOLING SPENT PLATING'SOLUTION TOPRECIPITATE RADIUM D AND LEAD CHLORIDES PLATI NG POLON I UM ON FOIL PREPARING FOIL FOR PLATING INCREASE IN POLONIUM CONTENT OF RADIUM D COMPOSITION ELAPSED TIME IN DAYS 2% 1/ 81rd u.-' -05$ 0-0 F; g 50 I00 I50 200 250 300 550 400 450 500 INVENTOR (JOHN H. DILLON ATTORNEYS Patented Aug. 26, 1941 RADIOACTIVE ALLOY John H. Dillon, Akron,

Firestone Tire & Ru Ohio, a corporation of Ohio, assignor to The bber Company, Akron, Ohio Application July 30, 1940, Serial No. 348,390

-3 Claims.

This application is a continuation-in-part of my co-pending application Serial No. 312,441, filed January 4, 1940.

This invention relates to radioactive alloys and relates especially to a radioactive alloy comprising a small but definite amount of a strongly ionizing radioactive metal.

Heretofore, radioactive alloys have not been commercially produced. A commercial use of radioactive alloys has only recently been suggested, making the development of a practical and effective allow desirable.

A primary object of the present invention is to provide a practical and efiective radioactive alloy.

Another object is to provide a radioactive alloy containing a small but definite proportion of a strongly ionizing radioactive metal.

Another object is to provide a practical nium alloy.

Further objects will be manifest from the specification, reference being had to the accom; panying drawings, in which:

Figure 1 is an elevation, partly in section, of apparatus suitable for carrying out certain steps in a preparation of radioactive alloys of the present invention;

Figure 2 is a flow-sheet of a method of preparing a polonium alloy of the type included in the invention; and

Figure .3 is a diagrammatic representation of the development of polonium by aging of radium D.

Broadly, the invention includes a new radioactive alloy, particularly one which comprises a relatively small proportion of a strongly ionizing radioactive metal. The term "strongly ionizing radioactive metal may be defined for the purposes of this invention as a radioactive metal which emits strong alpha rays at a practical rate and has a half life suificiently long to allow its practical utilization. The following naturally occurring substances are examples of strongly ionizing radioactive metals contemplated by the invention: polonium, radium, ionium, uranium II, protoactinium, radioactinium, actinium X, radiothorium and thorium X. Equivalents of the named naturally occurring substances, such poloas a metal having a strongly induced radioactivity of the alpha-emission type, are also contemplated for use in the invention.

The new radioactive alloy preferably contains a minor proportion of a strongly ionizing radioactive metal and a larger proportion of a nonradioactive metal from the group of elements having atomic numbers in the range of 22 to 28, inclusive. That is, the radioactive alloy contains a smaller proportion of the radioactive metal and a larger proportion of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, or a mixture of these metals. A preferred embodiment of the invention is a radioactive alloy comprising polonium and nickel suitable for spark plug electrodes.

In general, radioactive metals are very expensive because they are extracted with great difficulty from their ores, which are quite rare. However, it has been discovered that an alloy containing an exceedingly small proportion of a strongly ionizing radioactive metal possesses radioactive properties adequate for many purposes.

All radioactive materials give off one or more of three types of radiation called alpha, beta and gamma rays. The alpha rays, which are rapidly moving, doubly charged particles, are'much more' efficient for certain practical purposes, such as for ionizing gases, than either the bet-a rays (fast electrons) or gamma rays (electromagnetic radiation of extremely high frequency). Furthermore, the alpha rays are not dangerous to human beings, whereas gamma rays may be exceedingly harmful and require extreme safety precautions. The beta rays are also dangerous to some extent.

Hence, it is quite apparent that aradioactive material emitting only alpha rays is much to be preferred for certain commercial purposes.-

The relations between polonium (radium F), radium D, radium, and uranium are set forth .in the following Table I, showing the uraniumradium radioactive series and adapted from Landolt-Bomstein Physikalisch-Chemische Tabellen, fifth edition, published by Julius Springer, Berlin.

Table I Atomic st W k Element Half life g ria Wt. No.

92 4.4X10yrs Alpha... 90 24.5 days... Beta 01 1.17 mindo Gamma. 91 6.7 hrs do- 92 1.7X10 yrs-. Alpha... 90 85,000 yrs do 88 1690 yrs do Betaand gamma. 86 3.83 days do. 84 3.05 min do 82 26.8 min Beta. Gamma. 83 19.7 min. Betaand gamma 84 0.0002 sec Alpha 81 1.3 min Beta 82 22.3 yrs Betaand gamma. RadiumE 210 83 5.0 days Beta Radium F (polo- 210 84 138 days Alpha Gamma.

mum Radium G (lead) 206 82 Stable From Table I it is seen that polonium, sometimes known as radium F, occurs among the end transformation products of radium. Radon tubes, which are no longer suited for their original therapeutic functions, constitute a convenient source of polonium. Radon tubes are small ampules of glass or gold originally charged with the gaseous radon evolved by radium salts. The radon changes into short-lived radium C, which gives off powerful gamma rays and makes the radon tubes medicinally useful. After a few days of usefulness by virtue of the gamma ray emission the radon tubes are medicinally spent, since they contain practically no radon or radium 0. They now contain mainly the relatively stable solid radium D, which exists as a minute deposit on the inner walls of the tubes. After several months of aging an appreciable amount of polonium is contained in the tubes, formed from the radium D at the rate indicated by Figure 3.

Another source of greater commercial importance is the lead residue remaining after the extraction of radium from its ore. The lead residue is preferably treated to form the lead chloride salt. The resulting lead chloride contains all radioactive materials below radium C" in the above table, being rich in radium D (an isotope of lead), which slowly changes into radium E,

and containing appreciable radium F, or polonium. Radium E rapidly changes into polonium, as shown in Table I.

Polonium is of especial interest because it is the only known radioactive metal emitting the desirable alpha rays almost exclusively and at a practical rate and giving rise to no other radioactive element emitting undesired beta or gamma rays. The immediate transformation product of polonium, radium G, is an inactive isotope of ordinary lead. Thus no dangerous products develop from polonium, in contrast with radium, certain transformation products of the latter emitting strong beta and gamma radiation. Table I indicates that polonium emits feeble gamma rays in addition to strong alpha rays. It is well known that polonium emits only a few quanta of gamma rays for each million alpha rays (see H. C. Webster, Chemical Abstracts, 32, 1565-6 (1938)). Practically speaking, therefore, polonium emits only alpha rays.

In selecting a radioactive metal for use in preparing a practical radioactive alloy the radiation activity of the metal must be considered. A radioactive element changes into another ele.

ment according to an exponential law governed by the activity (number of rays per second) of the element. The selection of a metal of very low activity, such as uranium, would be unwise, because, even though it has the long half life (time required for one mass unit of the substance to be reduced to one-half mass unit) of approximately five billion years and emits only the desirable alpha rays; the activity of even the pure metal is too low to be of any practical value. On the other hand, radium A emits only alpha rays very copiously buthas a half life of only three minutes.

Polonium emits alpha rays at a rate in excess of 4500 times the alpha emission rate of pure radium, and has the reasonable half life of 138 days, which period of time is suflicient in many cases for the utilization of the strong alpha radiation of the substance. It is practicable to add sufiicient polonium to an alloy such that the alloy has useful radioactivity for many purposes several years after itis produced. Only a very minute quantity of polonium need be present in an alloy in order to render same of practical value. For example, a spark plug electrode alloy initially containing as little as two one-hundredmillionths of one per cent of polonium has been found to be effective in ionizing the gas in the gap of a spark plug for an internal combustion engine, at the end of two years, when the polonium content of the alloy has fallen to less than one-billionth of one per cent.

Although polonium is the preferred radioactive metal for use in the present invention for the reasons given above, certain other substances listed in Table I are strongly radioactive and are suitable for incorporating in the novel alloy. These additional substances are radium, ionium and uranium II. The three additional substances emit alpha rays at effective rates and have sufliciently long half-life periods to render them especially useful in alloys. However, in view of the fact that these substances or their transformation products also emit beta and gamma rays, it is necessary to handle an alloy containing one of them with proper precautions. Radium, ionium and uranium II occur in certain pitchblende deposits and each is extracted therefrom in a substantially pure form by known methods.

A second family of radioactive elements, the actinium series, is shown in Table II, and is adapted from the above-mentioned Landolt- Bernstein reference and Langes Handbook of Chemistry, pages 60 and 61, third edition, published in 1939 by Handbook Publishers, Inc., Sandusky, Ohio.

Table II Atomic Element I Half life 33,2 Wt. I No.

Actino-uranium. 235 92 4.0Xl0 Uranium Y 231 24 hrs. 31

231 91 227 89 Beta. 227 90 Do. 223 88 2l9 86 215 84 Actmlum B 211 82 Beta and Actinium C... 211 83 2.16 min.-. B ta. a. Actgruum C. 211 84 0.005 sec..-" Actimum C" 207 81 4.76 min Actiuium D (lead). 207 82 Stable Three metals listed in Table II are strongly radioactive in that they emit strong alpha rays at practical rates and have half-life periods sufficlently long-to render them useful in radioactive alloys. These metals are protoactinium, radloactinium and actinium X. Protoactinium is associated with uranium in pitchblende and carnotite, radioaetinium and actinium X also being present in these ores. Each of the three active substances can be separated from one of the ores by known methods. Usually, protoactinium' is separated first, and radioactinium and actinium X are separately removed from an aged Protoactinium preparation by known procedures.

A third family of radioactive elements, the thorium series, is set out in Table III and is adapted from the aforementioned Landolt-Bornstein reference.

Table III Weak rays Atomic Half life Element Wt. N o.

Thorium Mesothorium 1.. Mesothorium 2.-..

Radiothorium Thorium X Thoron Thorium A 1. Thorium B oococo c0000 man- Beta.

Thorium C Thorium C Thorium C Thorium D (lead)- Two of the substances shown in Table III, radiothorium and thorium X, are strongly radioactive metals, in that they emit strong alpha rays at relatively high rates and have half-life periods long enough to allow them to be successfully employed in radioactive alloys. Both' of these substances occur in thorium ores and may be separated therefrom by known methods. A convenient scheme for separating them in useful form is first to separate mesothorium 1 and thorium X together, employing this mixture where thorium X is desired. Radiothorium is formed, according to Table III, from the mesothorium 1, when this mixture-is allowed to age, and can be readily separated from the aged mixture by known methods. If a relatively pure thorium X is desired, it is obtained by known methods directly from an aged preparation of radiothorium free from mesothorium 1.

According to a preferred method of preparing the novel alloy, a strongly radioactive metal is first plated (by electrodeposition, electrochemical displacement, adsorption or vaporization) onto a base metal (in any convenient form such as, for example, plate, foil, wire, granules or powder). After determining the amount of plated radioactive metal, which amount can be relatively accurately predetermined, by any suitable measurement, as hereinafter described, the plated object is then melted with or without admixture of further base metal or other. metal in order to produce the desired alloy or mixture of metals.

Unweighable quantities of the radioactive substance to be alloyed may be measured by a combination of an electroscope and an ionization chamber which has previously been calibrated against a known amount of a radioactive substance or an absolute measuring apparatus. An example of the latter type of apparatus is the 75 The following specific example of a method for obtaining a plating of polonium and for making a polonium-base metal alloy is given for illustrative purposes only and is not to be construed as limiting the invention thereto:

Example The preferred commercial method of preparing a polonium alloy is illustrated in part by Figures 1 and 2 and is described in detail in the aboveidentified application Serial No. 312,441. The method comprises producing polonium-plated foil by plating polonium from a lead chloride solution containing same onto a suitable base metal foil, removing the plated foil from the solution, cooling the solution to precipitate lead chloride, sep

arating the precipitated lead salt from the mother liquor, aging the salt to develop ,more polonium (the aging time being dependent on economic considerations in view of the relationship shown in Figure 3), and then forming a solution of the aged salt in the mother liquor from a previous plating operation and plating polonium as before. The plated foil is added to a melt of a suitable base metal to form a polonium alloy.

An initial plating solution is formed by dis solving pounds of polonium-containing lead chloride in 300 gallons of boiling 0.03 normal hydrochloric acid contained in a tank i2, which is heated by the admission of steam into the jacket I4. Several thin nickel foils, 5 (a, b, etc.) which have been etched and washed in containers I and II, are suspended in the boiling plating solution i5 for about 4 to 5 hours to plate substantially all of the polonium from the solution onto the foils. The plated foils are then removed from the tank l2, washed, dried, and the polonium content determined by means of a Geiger counter or ionization chamber equipment. As soon as the plated foils have been removed from the tank I2, circulating water is substituted for steam in the jacket I4 to cool the tank contents to about 20 0., in order to precipitate most of the lead chloride from the plating solution. The precipitated lead chloride is scooped from the tank and placed in a container 2 (or 3, 4, etc.) to age. For a subsequent plating operation the aged contents I of container 2 (or 3, 4, etc.) are dissolved in the heated mother liquor retained in the tank 12, and the plating is conducted as above.

A radioactive nickel alloy was prepared by adding plated foils having a polonium content of 140.3 micrograms (from eight consecutive plating operations) to a sufiicient quantity of a molten nickel alloy containing about 3 percent of manganese to produce 1600 pounds of a polonium alloy. The required amount of the non-radioactive nickel alloy was placed in a suitable crucible and the latter was inserted in an electric induction furnace to melt the alloy. Then the plated foils were added to the melt and high frequency current was allowed to pass through the mixture for several seconds to insure thorough mixing of the metals. Thereafter the current was cut off, and the crucible was removed from the furnace. The resulting ingot of polonium-nickel alloy was found to have a polonium content of 0.08 microgram per pound, whereas the input of polonium to the melt had been 0.09 microgram per pound.

The above example and other examples disclosed in said application Serial No. 312,441 show the formation of alloys containing polonium in the range of approximately one-one hundred millionth of one per cent to one-one hundred thousandth of one per cent. Obviously an alloy containing even less polonium, such as one billionth of one per cent or less, can be prepared by melting the polonium-plated metal with an even larger proportion of the other metal. Likewise, an alloy containing a larger percentage of polonium than 0.00001 can be produced by melting a plated foil containing a larger proportion of polonium than shown by the foils described above. The invention contemplates radioactive alloys containing preferably less than 0.01 per cent of a strongly ionizing radioactive metal, since the use of an alloy containing more than this proportion of those radioactive metals emitting gamma rays is not practical from the standpoint of the wellbeing of the user. Moreover, an alloy containing less than 0.01 per cent of a strongly radioactive alloy has been found to be commercially feasible, whereas the cost of producing one containing a higher proportion of a strongly radioactive metal would be prohibitive from a, commercial standpoint.

Although the example shows the preferred use of nickel or a nickel-manganese alloy as the nonradioactive component of the radioactive alloys produced, a similar alloy may be produced in a similar manner by using any metal having an atomic number in the range of 22 to 28. These non-radioactive metals may be used in a substantially pure form or mixed with each other to form the major part of the alloy. Also, one of these metals may be used in admixture with various other metals. so long as the alloy so produced is substantially equivalent to the alloys hereinabove described.

An important result of the invention is that a practical and relatively cheap radioactive alloy is for the first time provided, and is of such nature that it can be readily and cheaply produced commercially and can be advantageously employed commercially, especially for use in an electrode for a gaseous discharge device, such as a spark plug.

Any workable method of forming a deposit, plating or coating of polonium on a base metal is satisfactory for the purposes of the present invention. Thus. polonium may be plated by electrochemical displacement onto any other metal having a higher electrode potential than p 1 nium (e. g., silver, copper, lead, nickel, cobalt and aluminum), although for practical reasons metals less electropositive than aluminum are preferred. Polonium may also be plated onto any suitable metal electrode by electrodeposition from a solution containing polonium. A coating of polonium may also be formed on a metal such as silver,

gold or platinum by adsorption from a solution comprising polonium. Furthermore, polonium may be vaporized or distilled onto another metal, preferably at a subatmospheric pressure. These methods apply also to the production of platings of other radio-active metals.

In additionto spent radon tubes and the lead residues attending the preparation of radium. other compositions containing polonium are contemplated for use inthe preferred method. Some other commercial compositions ornaturally occurring compositions, which contain appreciable proportions of polonium in the absence of material proportions of radium D or lead, are also suitable for use in obtaining polonium for preparing a radioactive alloy of the present invention.

Although it is thought that the mixtures of metals herein described as alloys are properly so designated, it has not been found possible to prove that a true alloy is always produced by the practice of the preferred method. Therefore, it is to be understood in the specification and appended claims that alloy means any substantial mixture of two or more metals, such as the product of the preferred method. Although it is thought that the radioactive alloy produced by the preferred method is a substantially uniform dispersion of the radioactive metal throughout the other components of the alloy, it is possible that some of the radioactive metal is ox dized during the alloying process, so that the alloy may contain a substantially uniform dispersion of the oxidized radioactive metal.

It is obvious that the preferred method described in detail hereinabove with reference to the production of a polonium alloy may be successfully applied to the production of other strongly ionizing radioactive alloys of the invention by making the necessary modifications apparent in each instance. The invention includes alloys of strongly ionizing radioactive metals no matter what may be their manner of production.

Obvious chemical equivalents may be substituted and other obvious modifications may be made without departing from the nature and spirit of the invention as defined in the appended claims.

What is claimed is:

1. A radioactive alloy comprising nickel and polonium, the polonium being present in the range of one one-billionth (0.000000001) per cent to one one-hundredth '(0..01) per cent, and the nickel constituting substantially all of the balance.

2. A radioactive alloy composed of from one billionth (0.000000001) per cent to one one-hundredth (0.01) per cent of a strongly ionizing radioactive metal of the group consisting of polonium, radium, ionium, uranium II, protoactinium, radioactinium, actinium X, radiothorium and thorium X, and the balance substantially all nickel.

3. A radioactive alloy comprising nickel and radium, the radium being present in the range of one one-billionth (0.000000001) per cent to one one-hundredth (0.01) per cent, and the nickel constituting substantially all of the balance.

JOHN H. DILLON. 

